Howdy Jon W and All,
I've been away from it for several years, but I worked at Scout summer camps for many summers and was a Scoutmaster for about 15 years. I only remember one instance of a scout wanting to listen to recorded music on the trail. I was able to work through that one, and Ididn't mind some of the other music in camp as long as it didn't invade somebody else's (most often mine) space. I was not so kind, and would subject everyone to my singing constantly. And people joined in very often including lots of teenagers.
I guess a certain firmness of attitude (we're going to do this whether you like it or not (and eventually you probably will end up liking it)), a really noticeable love of the songs and sharing them, and developing in as many scouts as possible the ability to lead at least one song themselves (always giving support to what was right, not criticism of what was wrong) led them to have enough confidence that I never had problems getting troops or camps full of scouts (and parents) to sing or to lead songs.
Most of it at summer camp was done at the dining hall (after the meal or waiting in line for the meal (not sharing the music always seemed like a real drawback to jamboree-style cooking instead of having a central dining hall)) with different staff members recruited to lead the songs (and eventually after enough years at a given camp, would get volunteers from campers and leaders); at ceremonies such as flag raising or lowering; and for the culmination, at campfire programs with (depending on the size of the camp) every patrol being responsible for doing a skit and/or leading a song (both at small camps and just the one they signed up for (as long as it was a balanced program) if it was a large camp. The idea that they were not the only ones having to get up and make fools of themselves made a real difference. Those campfire programs almost always followed the course of the campfire with building songs and activities at the beginning, bright and blazing things in the middle, and a couple of quiet songs and a story or two at the end with the Scoutmaster's (Campmaster's) Minute. The use of carefully chosen cheer master(s) to help recognize all but the final performance(s) (and here, a touch of criticism might find it's way in with dud cheers for dud performances) kept things going and added to the enthusiasm.
At the troop level, the same kinds of things would happen at campfires and ceremonies. Since I was able to help the scouts have fun with those, I was able to go the next step to get the PLC or TLC (or whatever initials are presently used for the scouts who lead the troop) to include a song in the opening and closing at each troop meeting so that they would have more material to draw upon for those campfire times. This also allowed the teaching of more songs.
The material came from the scout materials (Songbook, Boys' Life or Scouting, Roundtable helps, Cub Scout materials) or from my own folk-style background. I was usually about the only one who played an instrument, and I would introduce and use whatever I could lay my hands on from recorders to dulcimers to autoharp to guitars and more. There were even times when scouts brought their band or orchestra instruments along for special occasions and we would rehearse together.
But the overall key was that most of the songs were done a cappella, with plenty of repetition, started with easy or well-known things and worked into ones that took more ability or concentration, that scouts were given the chance (forced) to lead songs as soon as they seemed ready, encouraged to make a song their own so that they would have something to lead every time they needed to (until they decided to build a greater repertoire), and (I've left this out before) songs with motions were really encouraged so that even those who didn't sing (no confidence, voice changing, or that teacher who had told them that they couldn't sing) could still begin to participate and gradually gain confidence while keeping the new leader from feeling like the total center of attention since everyone else was also doing crazy things (and if the adult leaders refuse to do those crazy things, the scouts will also refuse and most of this will not work).
I led and introduced many songs (changing constantly) and used instrumental accompaniment when it seemed appropriate (but didn't rely on it all the time since I knew the scouts wouldn't learn to lead the songs if that was all they heard me do) and every once in a while accompanied somebody else if asked.
I knew I'd go on a long time here, but it's certainly too long now. There were some incredibly inspirational moments and great memories from all of that time singing in scouting, but that's another thread if anyone is interested.